In Chapter Two, amidst all the fighting over the right to speak and whether the conch means that everyone has to listen or not, Piggy is the one who comes up with the idea of building shelters.

He is pretty upset about the fact that their fire has gone out of control and that they can't seem to get anything right.  In the midst of his anger he also points out that they really ought to build some shelters since it is likely that they will be there for a long time before anyone comes to find them.  He is particularly upset given that they can't manage a fire so he feels confident they won't get rescued anytime soon.